The present invention relates to amplification-type solid state image pickup devices, and methods of using the same.
Amplification-type solid state image pickup devices employ picture elements which serve both to amplify a detected light signal and to output the amplified signal when scanned in accordance with a predetermined scanning sequence. Such image pickup devices include charge modulation devices (CMD) in the form of MOS-FET devices in which photoelectric charge is accumulated in the MOS gate.
The MOS-FET devices employ a polysilicon gate electrode disposed over a light-receiving region of the device. Consequently, the light is attenuated by the polysilicon gate electrode before it is able to reach the light-receiving region in order to be detected. A further drawback of the device is that short wavelength visible light is attenuated more severely so that the sensitivity of the device to blue light is considerably less than its sensitivity to longer wavelengths.
Although efforts have been made to minimize the thickness of the gate electrodes used in MOS-FET devices, the ability to reduce their thickness is limited, so that some light attenuation thereby inevitably occurs. Moreover, the gate electrode cannot be made substantially transparent, so that a considerable degree of light attenuation results as light passes through the gate electrode, resulting in the aforementioned reduced sensitivity.